European Journal of Cardiovascular Medicine

The autonomic nervous system (ANS) regulates various involuntary physiological functions, such as heart rate, blood pressure, and digestion. It consists of two components: the sympathetic nervous system, which is activated in response to stress, and the parasympathetic nervous system, which controls rest and recovery processes [1]. The balance between these two systems is crucial for maintaining cardiovascular and metabolic health.

Dietary patterns, particularly vegetarian and non-vegetarian diets, have been shown to influence overall health, with some studies suggesting that vegetarian diets can improve cardiovascular function due to the higher intake of antioxidants, fiber, and lower cholesterol levels [2]. In contrast, non-vegetarian diets, especially those rich in red and processed meats, have been associated with increased risks of hypertension, cardiovascular diseases, and inflammation [3]. However, there is limited research on how these diets impact ANS reactivity.

Heart rate variability (HRV) and other autonomic function tests are useful tools to assess autonomic balance, providing insights into parasympathetic and sympathetic activity[4]. This study investigates the autonomic nervous system reactivity in vegetarians compared to non-vegetarians through HRV, Valsalva ratio, cold pressor test, orthostatic test, and deep breathing test. Understanding these relationships could provide further evidence of the benefits of a vegetarian diet in promoting better autonomic function.

Study Design

A cross-sectional comparative study was conducted at [Institution Name]. Ethical approval was obtained from the institutional ethics committee, and informed consent was obtained from all participants.

Participants
The study included 200 healthy individuals, aged 20-50 years, divided into two groups:

• Group A: 100 vegetarians (those who had adhered to a vegetarian diet for at least 5 years)
• Group B: 100 non-vegetarians (those consuming meat at least twice a week for the past 5 years)

Exclusion criteria; included individuals with a history of diabetes, hypertension, cardiovascular disease, or any medication affecting autonomic function.

Autonomic Function Tests

To assess autonomic nervous system reactivity, the following tests were conducted:

1. Heart Rate Variability (HRV): Measured by electrocardiogram (ECG) at rest.
2. Valsalva Ratio: Participants performed a forced expiration, and the ratio of heart rate changes was calculated.
3. Cold Pressor Test: The subject immersed their hand in cold water, and changes in blood pressure were recorded.
4. Orthostatic Test: Blood pressure and heart rate were recorded upon standing after resting in a supine position for 5 minutes.
5. Deep Breathing Test: Heart rate variability in response to deep breathing was assessed.

Statistical Analysis

Data were analyzed using SPSS software. Results were presented as mean ± standard deviation (SD). Independent t-tests were used to compare the two groups, with a p-value < 0.05 considered statistically significant.

Table 1: Demographic Characteristics of Study Participants

The demographic characteristics between the vegetarian and non-vegetarian groups are quite similar. The mean age and BMI do not differ significantly between the two groups, as indicated by the high p-values (p > 0.05). Both groups also have an equal gender distribution (50 males and 50 females), ensuring balanced group comparison.

Table 2: Autonomic Function Test Results: Heart Rate Variability (HRV)

Heart rate variability (HRV) is higher in vegetarians (72.5 ms²) compared to non-vegetarians (64.3 ms²). The difference is statistically significant (p = 0.04), indicating better parasympathetic function in vegetarians. Higher HRV suggests a healthier autonomic balance, which could be due to the cardiovascular benefits associated with a vegetarian diet.

Table 3: Autonomic Function Test Results: Valsalva Ratio

The Valsalva ratio, a measure of heart rate response during forced expiration, is significantly higher in vegetarians (1.52) compared to non-vegetarians (1.44), with a p-value of 0.03. This suggests stronger parasympathetic reactivity and better cardiovascular control in the vegetarian group.

Table 4: Autonomic Function Test Results: Cold Pressor Test

The cold pressor test, which assesses sympathetic activation, reveals that non-vegetarians experienced a greater increase in both systolic and diastolic blood pressure compared to vegetarians. The difference is significant for both systolic (p = 0.02) and diastolic (p = 0.01) blood pressure, suggesting higher sympathetic reactivity in the non-vegetarian group, which might be linked to higher risks of cardiovascular stress.

Table 5: Autonomic Function Test Results: Orthostatic Test

The orthostatic test measures the change in blood pressure when a person stands up after lying down. Non-vegetarians experienced a more significant drop in systolic and diastolic blood pressure compared to vegetarians, with statistically significant p-values (0.04 for systolic and 0.03 for diastolic). This suggests poorer autonomic control in non-vegetarians, potentially making them more susceptible to dizziness or fainting upon standing.

Table 6: Autonomic Function Test Results: Deep Breathing Test

The heart rate change during the deep breathing test is significantly greater in vegetarians (18.2 bpm) compared to non-vegetarians (15.4 bpm), with a p-value of 0.03. This indicates better parasympathetic response in vegetarians, as deep breathing exercises typically stimulate parasympathetic activity.

*Significant at p < 0.05.

The results of this study reveal significant differences in autonomic nervous system reactivity between vegetarians and non-vegetarians, with vegetarians demonstrating better autonomic function across multiple tests.

Vegetarians exhibited higher heart rate variability (HRV) than non-vegetarians, indicating greater parasympathetic activity and a more balanced autonomic nervous system. HRV is often used as a marker of vagal tone, and higher values are associated with better cardiovascular health[5]. This finding aligns with previous research, which suggests that plant-based diets reduce oxidative stress and improve cardiovascular function[6].

In the Valsalva ratio test, vegetarians had a higher ratio than non-vegetarians, further indicating stronger autonomic reactivity and parasympathetic control. This test measures the reflexive heart rate response to a forced expiration and is often used to assess baroreceptor sensitivity[7]. The higher values in vegetarians may be linked to the beneficial effects of a diet rich in fiber, antioxidants, and unsaturated fats, which have been shown to improve vascular health[8].

The cold pressure test results showed that non-vegetarians experienced a more significant increase in systolic and diastolic blood pressure compared to vegetarians. This greater sympathetic activation in non-vegetarians suggests that meat-based diets may contribute to heightened cardiovascular reactivity and an increased risk of hypertension[9]. Studies have previously linked higher meat consumption with elevated risks of high blood pressure and sympathetic overactivity[10].

During the orthostatic test, non-vegetarians displayed a more pronounced drop in both systolic and diastolic blood pressure upon standing, indicating poorer autonomic control in maintaining blood pressure during postural changes. This is another marker of weaker autonomic balance, particularly in the regulation of blood pressure[11].

In the deep breathing test, vegetarians had a significantly higher heart rate change than non-vegetarians, suggesting better parasympathetic reactivity to breathing patterns. This supports the idea that vegetarian diets may improve autonomic flexibility and parasympathetic function[12].

The overall findings of this study suggest that vegetarians have better autonomic nervous system regulation compared to non-vegetarians, likely due to the beneficial cardiovascular and anti-inflammatory effects of plant-based diets. These results underscore the importance of diet in maintaining autonomic balance and reducing the risk of cardiovascular diseases.

The present study highlights significant differences in autonomic nervous system (ANS) reactivity between vegetarians and non-vegetarians. Through a comprehensive set of autonomic function tests, vegetarians demonstrated better autonomic regulation, with higher heart rate variability (HRV), greater Valsalva ratio, enhanced parasympathetic response during the deep breathing test, and a lower increase in blood pressure during the cold pressor test. These findings suggest that a vegetarian diet, rich in fiber, antioxidants, and unsaturated fats, may positively influence the balance between the sympathetic and parasympathetic nervous systems, contributing to improved cardiovascular and autonomic health.

In contrast, non-vegetarians exhibited higher sympathetic reactivity, particularly in response to stressors such as the cold pressor and orthostatic tests. This increased sympathetic activity could be associated with the cardiovascular risks typically linked to diets rich in meat and processed foods.

Overall, the results indicate that vegetarian diets may offer protective benefits for the autonomic nervous system and cardiovascular health, supporting the role of plant-based diets in promoting better health outcomes. These findings provide a foundation for future research and suggest that dietary patterns should be considered when assessing autonomic function and cardiovascular risk.

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